The invention concerns the operation of a nuclear reactor, particularly a pressurized-water reactor, with measuring probes for measuring the power density in the reactor core, and with control rods which are adjustable in the core for the purpose of power output control, individually or sequentially in groups, for maintaining a uniform power distribution over the cross section of the core. According to the German Auslegeschrift No. 1,244,307, such a nuclear reactor is equipped with rods of structurally uniform design, which are moved in dependence on the magnitude of the controlling signal individually or in groups, in steps and in cyclic sequence. The cyclic sequence, i.e., the number and local distribution of the control rods operated at a time, is determined by a program which is intended to provide a definite profile of the power distribution as a function of the depth of immersion of the control rods.
However, particularly in nuclear reactors of very large output of, for instance, 1200 MWe, uneven power distribution can result in such operation from the fact that local xenon poisoning reduces the power in individual parts of the reactor core. This can even excite oscillations in the power distribution, which lead to local overheating in the core even if the overall output of the nuclear reactor remains constant. It is therefore an object of the invention to find a method of power control for such nuclear reactors of large output, which takes the local power density into consideration in a better manner.